MIS transistor and method for producing same

ABSTRACT

In a MIS transistor, the top surfaces of source/drain regions (S/D diffusion layers) formed on a semiconductor substrate  1  are arranged nearer to a gate electrode than a channel plane on the semiconductor substrate, and the top surfaces of the source/drain regions are arranged nearer than the channel plane than the interface between a gate insulator film provided on the upper side of the channel plane and the gate electrode. In this transistor, a groove is selectively formed in the surface of the semiconductor substrate, and a polycrystalline silicon deposited in the groove may be used as a mask to form impurity diffusion layers serving as source/drain regions to laminate and form a gate insulator film of a high dielectric film and a gate electrode. Alternatively, the polycrystalline silicon may be selectively formed to be used as a mask to elevate and form the impurity diffusion layer to laminate and form the gate insulator film and the gate electrode. Thus, it is possible to achieve both of the reduction of the resistance of the S/D diffusion layers and the reduction of the gate parasitic capacitance.

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to a MIS transistor and amethod for producing the same. More specifically, the invention relatesto a MIS transistor having a large driving current and a small parasiticcapacitance, and a method for producing the same.

[0002] As a request to achieve the scaling down of a transistor havingthe metal insulator semiconductor (MIS) structure grows more intense,the scaling down of the MIS transistor progresses steadily at present.The scaling down of the MIS transistor is carried out by using atechnique called a scaling rule for forming a source/drain region inproportion to a gate length, specifically by reducing the junction depthof an impurity diffusion region, a so-called diffusion layer, which isto be a drain and/or source, as the gate length decreases when the gatelength decreases.

[0003] However, in a fine transistor having a gate length of less than0.2 μm, the depth (Xj) of diffusion is too small, so that there is aproblem in that the resistance of the gate increase to increase theparasitic resistance of the whole transistor to reduce a substantialdriving current. In order to reduce the parasitic resistance, it ispossible that the depth of the junction is reduced when the metalsilicidation of the source and drain to be introduced is carried out.However, when the reduction of the depth of the junction is too great,there is a problem in that the silicide metal does not remain in thediffusion layer and penetrates the substrate to cause the junction leak.

[0004] The problem in that the resistance increases or the silicidationis difficult to carry out when the junction is shallow has been solvedby the art called an elevated source/drain, a concave transistor, arecessed channel transistor or the like. This transistor has a structurewherein the surfaces of the source and drain are higher than the channelsurface of the transistor (e.g., S. M. Sze Physics of SemiconductorDevices second edition, 1981, pp490). FIG. 1 shows a MIS transistorwhich has such a concave MOS structure and which comprises asemiconductor substrate 1, source/drain regions 2, a channel planearranged therebetween, an SiO₂ film 51 provided on the top of thechannel plane 7, and a gate electrode 6 facing the channel plane via theSiO₂ film 51.

[0005] In FIG. 1, each of the source/drain regions 2 include a firstimpurity diffusion region 2 a formed in the semiconductor substrate 1(below the channel plane 7 in the drawing), and a second impuritydiffusion region 2 b laminated outside of the channel plane 7 (above thechannel plane 7 in the drawing). Such a structure wherein the gateelectrode 6 is surrounded by the second impurity diffusion regions 2 bvia the SiO₂ film 51 may be considered as a construction wherein agroove is formed in the source/drain regions 2 or as a constructionwherein the second impurity diffusion regions 2 b are elevated.

[0006] However, in the conventional MIS transistor having the structureshown in FIG. 1, the gate electrode 6 is surrounded by the source/draindiffusion layer 2 via the SiO₂ (insulator) film 51, so that there is aproblem in that the gate-to-drain capacitance and source-to-draincapacitance increase, so that the switching speed of the transistordeteriorates to a large extent.

[0007] As described above, in the conventional MIS transistor, there isa problem in that it is not possible to reduce both of the resistance ofthe source/drain diffusion layer and the gate parasitic capacitance.

SUMMARY OF THE INVENTION

[0008] It is therefore an object of the present invention to eliminatethe aforementioned problems and to provide a MIS transistor and a methodfor producing the same, capable of reducing both of the resistance of asource/drain diffusion layer and a gate parasitic capacitance.

[0009] In order to accomplish the aforementioned and other objects,according to a first aspect of the present invention, a MIS transistorbasically comprises a semiconductor substrate, source/drain regionsformed on the substrate, and a gate electrode provided above a channelregion between the source/drain regions, the top surfaces of thesource/drain regions formed on the semiconductor substrate beingarranged toward the gate electrode from a reference plane of a channelplane in the semiconductor substrate, and the top surfaces of thesource/drain regions are arranged toward the channel plane from areference plane of an interface between a gate insulator film formed onthe channel plane and the gate electrode.

[0010] In the MIS transistor according to the first aspect of thepresent invention, a groove may be formed in the top surface of thesemiconductor substrate and has a bottom surface serving as the channelplane, the gate insulator film being formed in an opening of the groovevia a protective film, the gate electrode being arranged on the top ofthe gate insulator film, the source/drain regions being arranged on bothsides of the channel plane, so that a predetermined relationship betweenthe top surfaces of the source/drain regions, the channel plane and theinterface is established.

[0011] In addition, in the MIS transistor according to the first aspectof the present invention, the top surfaces of the source/drain regionslaminated in places which sandwich the channel plane on thesemiconductor substrate therebetween may be arranged toward the gateelectrode from a reference plane of the channel plane, and the topsurfaces of the source/drain regions may be arranged toward the channelplane from a reference plane of the interface between the gate insulatorfilm formed on the channel plane via a protective film and the gateelectrode.

[0012] Moreover, in the MIS transistor described in the above paragraph,the top surfaces of the source/drain regions provided so as to sandwichthe channel plane therebetween may be elevated from the channel plane tobe arranged on the side of the gate electrode, and the top surfaces ofthe source/drain regions may have a substantially flat surface having alevel which is elevated and arranged on the side of the gate electrode,and an inclined surface which is inclined from the level of the flatsurface to a level of the channel plane.

[0013] In addition, in the MIS transistor according to the first aspectof the present invention, the gate electrode surrounded by the gateinsulator film provided on the upper side of the channel plane may havea cross section of a T shape, the lower side of which is tapered.

[0014] According to a second aspect of the present invention, a MIStransistor basically comprises a semiconductor substrate, source/drainregions formed on the substrate, and a gate electrode provided above achannel region between the source/drain regions, the top surfaces of thesource/drain regions provided so as to sandwich the channel planetherebetween being elevated from the channel plane to be arranged on theside of the gate electrode, and the top surfaces of the source/drainregions having a substantially flat surface having a level which iselevated and arranged on the side of the gate electrode, and an inclinedsurface which is inclined from the level of the flat surface to a levelof the channel plane, the gate electrode surrounded by the gateinsulator film provided on the upper side of the channel plane having across section of a T shape, the lower side of which is tapered via astep portion.

[0015] According to a third aspect of the present invention, there isprovided a method for producing a MIS transistor comprising asemiconductor substrate, source/drain regions formed on the substrate,and a gate electrode provided above a channel region between thesource/drain regions, the method comprising the steps of: selectivelyforming an oxide film on the semiconductor substrate; using theselectively formed oxide film as a mask to carry out etching to form agroove; laminating a semiconductor layer in the groove to polish the topsurfaces of the oxide film and the semiconductor film, and thereafter,removing the oxide film; using the semiconductor film as a mask todiffuse an impurity in the surface of the semiconductor substrate toform a grooved impurity diffusion region including the bottom of thegroove; arranging a gate insulator film of a high dielectric film in agroove portion of the grooved impurity diffusion region so that the topsurface of the gate insulator film is arranged farther from thesemiconductor substrate than the top surface of the impurity diffusionregion other than the groove portion; and forming a gate electrode onthe top surface of the gate insulator film.

[0016] According to a fourth aspect of the present invention, there isprovided a method for producing a MIS transistor comprising asemiconductor substrate, source/drain regions formed on the substrate,and a gate electrode provided above a channel region between thesource/drain regions, the method comprising the steps of: selectivelyforming a semiconductor layer on the semiconductor substrate; using theselectively formed semiconductor layer as a mask to diffuse an impurityin the surface of the semiconductor substrate to form an impuritydiffusion region including an elevated impurity diffusion regionelevated from a channel plane which is formed on the surface of themasked semiconductor substrate; forming an oxide film on the side of thesurface of the elevated impurity diffusion region to use thesemiconductor layer as a stopper to polish the surface of the oxidefilm, and thereafter, removing the semiconductor layer; forming a gateinsulator film of a high dielectric film in a region surrounded by theelevated impurity diffusion region and the oxide film so that the topsurface of the gate insulator film is arranged farther from thesubstrate than the interface between the impurity diffusion region andthe oxide film; and forming a gate electrode on the top surface of thegate insulator film.

[0017] According to a fifth aspect of the present invention, there isprovided a method for producing a MIS transistor comprising asemiconductor substrate, source/drain regions formed on the substrate,and a gate electrode provided above a channel region between thesource/drain regions, the method comprising the steps of: selectivelydepositing semiconductor layers serving as source/drain regions, whichsandwich a region serving as a channel plane on the semiconductorsubstrate therebetween, so that an inclined surface is formed betweenthe top surface of the semiconductor layers and the channel plane;forming a dummy gate insulator film and a dummy gate electrode includinga second semiconductor layer on the channel plane, which borders theselectively formed semiconductor layers, by a technique including atleast a lithography; using the second semiconductor layer as a mask todiffuse an impurity in the surface of the semiconductor substrate toform impurity diffusion regions; removing the dummy gate electrode,which is formed on a portion serving as the channel plane sandwichedbetween the impurity diffusion regions, by etching; depositing aninsulator film of a high dielectric film on the whole surface of theexposed channel plane to form a gate insulator film, which has a crosssection of a grooved space at the center thereof; and depositing a gateelectrode on the top surface of the gate insulator film, which is formedon the whole surface so as to have a grooved space at the centerthereof, to form a gate electrode having a cross section of a T shape.

[0018] As described above, in a MIS transistor according to the presentinvention, a gate insulator film of a high dielectric film and a grooveor source/drain elevated structure are used, and a gate electrode havinga capacitor reduced thickness equal to a capacitor reduced thicknessobtained by dividing a real thickness of the gate insulator film by anaverage dielectric constant is provided so that the bottom surface ofthe gate electrode is arranged at a higher position than the surface ofa semiconductor substrate by a greater amount than the real thickness ofan insulator film between the gate electrode and a source/drain. Thus,it is possible to achieve both of the reduction of the resistance of thediffusion layer of the source/drain and the reduction of the gateparasitic capacitance.

[0019] In addition, in a MOS transistor according to the presentinvention, the average dielectric constant of a first insulator filmserving as the gate insulator film may be higher than the averagedielectric constant of a second insulator film for insulating the topsurface of the groove from the gate material.

[0020] Moreover, in such a MOS transistor, the first insulator filmserving as the gate insulator film may have a laminated structure of aninsulator film, which has a higher dielectric constant than that of anSiO₂ film, and a buffer insulator film for protecting the insulatorfilm.

[0021] In addition, in the above described MIS transistor, the bottomsurface of the gate electrode may be arranged at a higher position thanthe surface of the semiconductor substrate by a greater amount than thereal thickness of the semiconductor insulator having a capacitor reducedthickness which is equal to a capacitor reduced thickness obtained bydividing the real thickness of the gate insulator film by an averagedielectric constant. As described above, according to the presentinvention, it is possible to achieve both of the reduction of theresistance of the diffusion layer of the source/drain and the reductionof the gate parasitic capacitance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In the drawings:

[0023]FIG. 1 is a sectional view of a conventional MIS transistor;

[0024]FIG. 2 is a sectional view of the first preferred embodiment of aMIS transistor according to the present invention;

[0025]FIGS. 3A through 3E are sectional views showing steps of a methodfor producing the first preferred embodiment of a MIS transistoraccording to the present invention;

[0026]FIGS. 4A through 4E are sectional views showing steps of a methodfor producing the second preferred embodiment of a MIS transistoraccording to the present invention;

[0027]FIG. 5 is a sectional view of the third preferred embodiment of aMIS transistor according to the present invention;

[0028]FIGS. 6A through 6E are sectional views showing steps of a methodfor producing the fourth preferred embodiment of a MIS transistoraccording to the present invention;

[0029]FIG. 7 is a sectional view of the fourth preferred embodiment of aMIS transistor according to the present invention;

[0030]FIG. 8 is a sectional view of the fifth preferred embodiment of aMIS transistor according to the present invention;

[0031]FIGS. 9A through 9E are sectional views showing steps of a methodfor producing the fifth preferred embodiment of a MIS transistoraccording to the present invention;

[0032]FIG. 10 is a sectional view of the sixth preferred embodiment of aMIS transistor according to the present invention;

[0033]FIG. 11 is a sectional view of the seventh preferred embodiment ofa MIS transistor according to the present invention;

[0034]FIGS. 12A and 12B are plan views of the semiconductor device shownin FIG. 11; and

[0035]FIGS. 13A through 13E are sectional views showing steps forproducing the seventh preferred embodiment of a semiconductor deviceaccording to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Referring now to the accompanying drawings, the preferredembodiments of a MIS transistor and a method for producing the sameaccording to the present invention will be described in detail below.

[0037]FIG. 2 is a schematic sectional view of the first preferredembodiment of a MIS transistor according to the present invention.Furthermore, hatching is omitted from the drawings to make theindication thereof clear. The components or constituents having the samereference numbers as those in FIG. 1 denote components or constituentswhich are the same as or similar to those of the conventional MIStransistor.

[0038] In FIG. 2, reference number 1 denotes a semiconductor substrate.On the surface of the semiconductor substrate 1, impurity regions 2serving as source/drain regions are provided via a channel region 7.When the transistor operates, one of the impurity regions 2 serves as adrain electrode, and the other impurity region 2 serves as a sourceelectrode. Above the channel plane 7 between the impurity regions 2, arecessed portion or groove 4 is formed. In the groove 4, a highdielectric gate insulator film 5 is provided via a protective film 3. Onthe top of the high dielectric gate insulator film 5, a gate electrode 6is provided. The impurity regions 2 serving as the source/drain regionsare insulated from the gate electrode by an insulator film 13. The highdielectric gate insulator film 5 has a higher dielectric constant than3.9 which is the relative dielectric constant of the SiO₂ film of theconventional MIS transistor shown in FIG. 1.

[0039] In the above described construction, it is important that thelevel La of the top surface of the source/drain between the secondimpurity diffusion region 2 b and the insulator film 3 is arrangedfarther from the semiconductor substrate 1 than the level Lb of thechannel plane 7, and nearer to the semiconductor substrate 1 than thelevel Lc of the bottom surface of the gate electrode 6.

[0040] Similar to the conventional MIS transistor shown in FIG. 1, theimpurity regions 2 include a first impurity diffusion region 2 a formedin the semiconductor substrate 1 (below the channel plane 7 in thedrawing), and a second impurity diffusion region 2 b laminated outsideof the channel plane 7 (above the channel plane 7 in the drawing). Theprotective film 3 is formed of, e.g., a SiN or oxynitride film, forprotecting the gate insulator film 5. The protective film 3 includes afirst protective film 3 a arranged between the channel plane 7 and thegate insulator film 5, and a second protective film 3 b arranged betweenthe second impurity diffusion region 2 b and the gate insulator film 5.

[0041] With this construction, in the first preferred embodiment of aMIS transistor according to the present invention similar to theconventional MIS transistor of FIG. 1, the impurity diffusion regionsserving as the source/drain regions are formed so as to be elevated fromthe channel plane 7 forming a channel, through which a current passes,by the thickness of the second impurity diffusion region 2 b opposite tothe semiconductor substrate 1. Therefore, the resistance of thediffusion layer can be lower than with that in a case where thesource/drain regions are formed only in the first impurity diffusionregion 2 a below the channel plane 7. It is also possible to prevent thejunction leak, which is caused by the intrusion of silicidation to thejunction surface, from being caused when a silicide of nickel (Ni),titanium (Ti) or the like is formed.

[0042] In addition, the bottom surface 8 of the gate electrode 6 isarranged at a higher position than the top surface of the impuritydiffusion regions 2 serving as the source/drain regions, i.e., apartfrom the semiconductor substrate 1, so that the capacitance between thegate electrode and the source/drain, which deteriorates the performanceof the transistor, can be considerably reduced in comparison with theconventional concave MOS shown in FIG. 1. Moreover, the distance betweenthe gate electrode 6 and the source/drain electrode 2 b can be greaterthan that of the conventional concave MOS, so that it is possible tohold a small electric field. Therefore, it is possible to reduce aleakage current between the gate electrode 6 and the source/drainelectrode 2 b to prevent the dielectric breakdown. This feature isapplied to all of preferred embodiments which will be described below.

[0043] In a conventional MIS transistor (not shown) wherein a channelplane and the top surfaces of source/drain regions are arranged on thesame plane, if a gate insulator film provided between a gate electrodeand the channel plane is formed of an SiO₂ film, the bottom surface 8 ofthe gate electrode 6 is higher than the plane 7 from the thickness of52, and an insulator film for insulating the gate electrode from thesource/drain regions is formed of an SiO₂ film, so that it is possibleto reduce the parasitic capacitance in comparison with that of theconventional plane type MOS transistor.

[0044] For example, in the prior art, the gate length is 0.1 microns,the gate oxide film is scaled so as to have a thickness of about 3 nm.On the other hand, according to the present invention, when a device isdesigned by a protective film of Ta₂O₅ having a relative dielectricconstant of about 25 and SiN (relative dielectric constant=7.5) having athickness of 1 nm, if the reduced thickness of SiO₂ is maintained to be3 nm in order to have the same surface charge density Qs of transistors,the real thickness of SiN of a first protective film 3 a is 1 nm, sothat the reduced thickness of SiO₂ is “1 nm×3.9/7.5=0.52” nm. Moreover,the reduced thickness of SiO₂ of the high dielectric gate insulator film5 (Ta₂O₅) is “3 nm−0.52 nm=2.48 nm”, so that the real thickness is “2.48nm×25/3.9=15.9 nm”.

[0045] That is, if the depth of the groove of the impurity diffusionregion serving as the source/drain region is “15.9 nm (corresponding tothe thickness of the gate insulator film 5)+1 nm (corresponding to thethickness of the protective film 3 a)=16.9 nm”, the bottom surface 8 ofthe gate electrode 6 has the same level as that of the surface of thesource/drain region, and if the depth is 13.9 nm, it has substantiallythe same parasitic capacitance as that of a MOS transistor using anoxide film having a thickness of 3 nm on a conventional scaling trend.According to the conventional scaling, the depth of the diffusion of 0.1micron transistor is about 40 nm, so that the thickness of the diffusionlayer can be increased by 13.9 nm, i.e., 35%, to reduce the parasiticresistance thereof.

[0046] Assuming that the relative dielectric constant of SiO₂ is ε, thethickness of the SiO₂ film being TSiO₂, the relative dielectric constantof the high dielectric gate insulator film 5 being ε5, the realthickness thereof being T5, the relative dielectric constant of theprotective film 3 being ε3, and the real thickness thereof being T3,then a thickness for providing the same parallel plane capacitance asthat of the SiO₂ film having the thickness of TSiO₂ should meet thefollowing formula.

TSiO₂/εSiO₂ =T3/ε₂ +T5/ε₅

[0047] If the protective film is formed of an SiN film having athickness of 1 nm and if the relative dielectric constants of SiO₂ andSiN are 3.9 and 7.5, respectively, T5=ε5 (TSiO₂/3.9−1/7.5) (nm).Therefore, assuming that the thickness on the conventional scaling trendis TSiO₂ and that the depth of the groove for providing the sameparasitic capacitance is set so that the insulator material between thegate and the source/drain is SiO₂ or a material having the samedielectric constant as that of SiO₂, the following formula isestablished.

Dconcave=ε ₅ (TSiO₂/3.9−1/7.5)−TSiO₂

[0048] Thus, as the groove is shallower, the parasitic capacitance issmaller. When a titanium oxide film, TiO₂ film, which has a relativedielectric constant of about 80, which is thermally stable and whichneeds no protective film, is used, then the following formula isestablished similar to the same calculation as that when the protectivefilm is removed.

[0049]Dconcave=ε ₅×TSiO₂/3.9−TSiO₂

[0050] If the depth of the groove is 58.5 nm, it has the same parasiticcapacitance as the conventional MOS transistor using an oxide film of athickness of 3 nm, and it is possible to increase the thickness of thediffusion layer by 150% and to reduce the parasitic resistance incomparison with the case where a conventional diffusion layer having adepth of 40 nm is used.

[0051] Referring to FIGS. 3A through 3E, a method for producing thefirst preferred embodiment of a MIS transistor according to the presentinvention will be described. First, as shown in FIG. 3A, an SiO₂ film 9is deposited on a silicon substrate serving as a semiconductor substrateto be etched by a lithography. Then, using an SiO₂ film 9 as a mask, agroove 4 is formed by the reactive ion etching (RIE) (FIG. 3B).

[0052] Then, as shown in FIG. 3C, after a thin sacrificial oxide film 11is laminated on the surfaces of the SiO₂ film 9 and the groove 4 of thesilicon substrate, a polycrystalline silicon 10 is deposited to beplanarized to the top surface of the SiO₂ film 9 using the chemicalmechanical polishing (CMP) method or the etch back. At this time, thelamination of the thin sacrificial oxide film 11 is used for separatingthe polycrystalline silicon 10 from the silicon substrate 11.

[0053] Then, as shown in FIG. 3D, after the silicon oxide (SiO₂) film 9is removed, the polycrystalline silicon 10 is used as a mask to form asource/drain region 2 using the ion implantation or solid phasediffusion technique. Then, the polycrystalline silicon 10 and thesacrificial oxide film 11 are removed by, e.g., the chemical dry etching(CDE). Thereafter, as shown in FIG. 3E, an SiN film 3 serving as aprotective film is deposited or formed by the heat nitriding. Then, ahigh dielectric film 5 is formed by a sputtering technique, and a gateelectrode 6 is deposited. Finally, a silicon (Si) oxide film 12 isformed to produce a semiconductor device having the same structure asthat of the MIS transistor shown in FIG. 2.

[0054] Referring to FIGS. 4A through 4E, a method for producing thesecond preferred embodiment of a MIS transistor according to the presentinvention, and the construction thereof will be described below. First,referring to FIGS. 4A through 4E, the method for producing the MIStransistor will be described.

[0055] A dummy polycrystalline silicon 10 is formed on a semiconductorsubstrate 1 shown in FIG. 1 via a sacrificial oxide film 11 to bepatterned. Moreover, after oxidation is carried out so that the dummypolycrystalline silicon 10 is surrounded by an oxide film, asource/drain region 2 is formed by the ion implantation or the like asshown in FIG. 4B.

[0056] Then, after the silicon is elevated by the selective epitaxialgrowth technique, an impurity is implanted into the elevated portionagain by the additional ion implantation to be diffused. In the methodfor producing the first preferred embodiment of a MIS transistoraccording to the present invention, the groove 4 is first formed, andthe impurity is implanted into the groove from the top to be diffusedtherein, so that it is difficult to control the depth of thesource/drain region 2. On the other hand, in method for producing thesecond preferred embodiment of a MIS transistor according to the presentinvention, the depth of the source/drain region 2 underlying the channelplane 7 is determined by the degree of impurity implanted from thechannel plane 7, so that there is an advantage in that control is easy.

[0057] Then, a silicon (Si) oxide film 12 is deposited on thesource/drain region 2 while leaving the polycrystalline silicon 10, andthe silicon oxide film 12 is planarized to the top surface of thepolycrystalline silicon 10 by the CMP technique using thepolycrystalline silicon 10 as a stopper. As shown in FIG. 4C, thepolycrystalline silicon 10 and the sacrificial oxide film 11 are peeledoff by the CDE or the like, and a silicon nitride (SiN) protective film3 is deposited on a region extending from the side surfaces of thesilicon oxide film 12 and source/drain region to the top surface of thechannel plane 7.

[0058] Then, as shown in FIG. 4D, a high dielectric gate insulator film5 is deposited to a higher level than that of the top surface of thesource/drain region 2 by the sputtering, CVD or the like. When such aprocess is adopted, if the thickness of the high dielectric gateinsulator film 5 is smaller than the depth of the groove, the gateelectrode must be insulated from the source/drain by the protective film3, so that the protective film 3 must be thicker than that in a casewhere the level of the high dielectric gate insulator film 5 is higherthan that of the groove 4 in this preferred embodiment.

[0059] Then, as shown in FIG. 4E, a gate electrode 6 is deposited on thetop of the high dielectric gate insulator film 5 to substantially thesame level as that of the silicon oxide film 12 by the sputtering, CVDor the like. As described above, if the thickness of the high dielectricgate insulator film 5 is smaller than the depth of the groove, the gateelectrode 6 is arranged nearest to the top surface of the source/drainregion 2 only via the protective film 3, and the dielectric breakdownvoltage of this portion is critical. Thus, in this state, it has beenset to meet the following formula from its electric characteristics.

Dconcave=ε ₅ (TSiO₂/3.9−1/7.5)−TSiO₂

[0060] Therefore, it is desired that the groove portion be shallower inorder to improve the dielectric breakdown voltage of the transistor. Itis also desired that the thickness of the protective film 3 in the upperportion of the groove be thicker than that in the lower portion thereofin order to improve the dielectric breakdown voltage. This can beachieved by slightly etching and back filling a portion between the highdielectric gate insulator film 5 and the source/drain region 2 by theCDE or the like in the step of FIG. 4D.

[0061] According to the above described method for producing the secondpreferred embodiment of a MIS transistor according to the presentinvention, it is possible to obtain transistors having substantially thesame construction after a different process from the producing method ofthe first preferred embodiment for forming the source/drain region 2after forming the groove 4 using the SiO₂ film as a mask. However, thereis a difference only between the considerations that the groove 4 isformed on the top surface of the substrate 1 and that the source/drainregion 2 is formed on the substrate 1 to further elevate thesource/drain region 2 from the level of the channel plane 7.

[0062] In both of the first and second preferred embodiments of a MIStransistor according to the present invention, while the protective film3 has been formed between the high dielectric gate insulator film 5 andthe source/drain region 2, there are some cases where it is not requiredto provide the protective film 3 by controlling the material of the highdielectric gate insulator film 5 or by decreasing the temperature in theprocess. FIG. 5 shows the third preferred embodiment of a MIS transistoraccording to the present invention, wherein no protective film 3 isprovided. In FIG. 5, a protective film (the protective film 3 a in FIG.2) is not provided between a channel plane 7 of a silicon substrate 1serving as a semiconductor substrate and a high dielectric gateinsulator film 5, so that a protective film 3 b is provided only betweenthe side wall of the gate insulator film 5 and a second impuritydiffusion region 2 b.

[0063] Referring to FIGS. 6A through 6E, a method for producing thefourth preferred embodiment of a MIS transistor according to the presentinvention will be described below. Basically, the steps of FIGS. 6Athrough 6C are substantially the same as those in the method forproducing the first or second preferred embodiment of a MIS transistoraccording to the present invention. Then, a sacrificial oxide film 11and a polycrystalline silicon 10, which are shown in FIG. 6B, are peeledoff by the CDE or the like. Then, a silicon nitride (SiN) protectivefilm 3 is deposited in a region extending from the side surfaces of asilicon oxide film 12 and source/drain region 2 to the top surface of achannel plane 7, and a high dielectric gate insulator film 5 isdeposited by the CVD or sputtering.

[0064] Then, as shown in FIG. 6C, the high dielectric gate insulatorfilm 5 deposited by the CVD or sputtering is planarized to the topsurface of the oxide film 12 using the CMP technique. In a method forproducing the third preferred embodiment of a MIS transistor accordingto the present invention, the thickness of the high dielectric gateinsulator film 5 is determined by the thickness of the silicon oxidefilm 12 and the depth of the groove 4, so that there is an excellentadvantage in that it is easy to control the thickness.

[0065] However, in the case of a method for producing the fourthpreferred embodiment of a MIS transistor according to the presentinvention, the gate electrode 6 is formed by carrying out thelithography again, it is difficult to self-align the gate electrode 6 inthe groove 4. Thus, as shown in FIG. 6E, the gate electrode 6 is formedso as to be greater than the area of the opening of the groove 4.Therefore, although the parasitic capacitance of the gate electrode isslightly increased, the silicon oxide film 12 is sufficient thick, andthe dielectric constant of the silicon oxide film 12 is also small, sothat it does not have a great influence.

[0066]FIG. 7 shows a cross section of the fourth preferred embodiment ofa MIS transistor according to the present invention, which is producedby the method shown in FIGS. 6A through 6E. In FIG. 7, the MIStransistor comprises: a silicon substrate serving as a semiconductorsubstrate; a source/drain region 2 including a first impurity diffusionregion 2 a arranged nearer to the substrate 1 than a channel plane 7,and a second impurity diffusion region 2 b arranged toward a gateelectrode 6 from a reference plane of the channel plane 7; a siliconoxide film 12; a protective film 3 on the inner wall of a groove 4formed in the silicon oxide film 12 and second impurity diffusion region2 b; a high dielectric gate insulator film 5 formed in the groove 4 viathe protective film 3; and the gate electrode 6 formed so as to have agreater area than that of a region surrounded by the protective film 3on the gate insulator film 5.

[0067] Furthermore, while the gate electrode 6 has been had the samewidth as that of the gate insulator film 5 arranged in the groove 4 inthe above described first through third preferred embodiments of a MIStransistor according to the present invention and while the gateelectrode 6 has been wider than that of the gate insulator film 5 due tothe difficulty of self-alignment in the fourth preferred embodiment of aMIS transistor according to the present invention, the present inventionshould not be limited thereto, but the invention may be applied to atransistor wherein a gate electrode 6 is provided with side walls in,e.g., the lightly doped drain (LDD) structure, in the fifth preferredembodiment of the present invention which is shown in FIG. 8.

[0068] In FIG. 8 showing the fifth preferred embodiment of a MIStransistor according to the present invention, reference number 1denotes a silicon substrate serving as a semiconductor substrate, 7denoting a channel plane, 2 denoting a source/drain region including afirst impurity diffusion region 2 a and a second impurity diffusionregion 2 b, 3 denoting a protective film, 5 denoting a high dielectricgate insulator film, 6 denoting a gate electrode, and 8 denoting a sidewall of silicon dioxide (SiO₂) provided around the gate electrode 6.

[0069]FIGS. 9A through 9E show sectional views showing steps of a methodfor producing the fifth preferred embodiment of a MIS transistoraccording to the present invention. As shown in FIG. 9A and 9B, an SiNfilm 3 a serving as a gate insulator film, a high dielectric film 5 of,e.g., Ta₂O₅, a TiN film serving as a gate electrode, and apolycrystalline silicon 6 are sequentially deposited on a semiconductorsubstrate 1, and etching is carried out to form a portion serving as agate electrode from the polycrystalline silicon 6 as shown in FIG. 9C.Then, as shown in FIG. 9D, a side wall 8 of SiO₂ is formed so as tosurround the gate electrode 6 by the CVD or the like, and the gateelectrode 6 and the side wall 8 are used as a mask to form a gateinsulator film 5 by the CDE or the like.

[0070] Finally, as shown in FIG. 9E, after etching is carried out usingthe laminated structure of the gate electrode 6 of polycrystallinesilicon, the side wall 8 and the gate insulator film 5 is as a mask, aside wall insulator film 3 b is formed, and the source/drain is elevatedto form an electrode 2 b. Thereafter, a source/drain region 2 is formedby the ion implantation and solid phase diffusion. Similar to the firstthrough fourth preferred embodiments, the source/drain region 2comprises: a first impurity diffusion region 2 a arranged in thesubstrate 1 from the channel plane 7; and a second impurity diffusionregion 2 b which is arranged nearer to the gate electrode 6 than thechannel plane 7 and the top surface of which is lower than the bottomsurface of the gate electrode 6.

[0071] The fifth preferred embodiment of a MIS transistor according tothe present invention, which is formed according to the process shown inFIGS. 9A through 9E, has the structure shown in FIG. 8. That is, theperipheral surfaces, i.e., at least the bottom surface and sidesurfaces, of the high dielectric gate insulator film 5 are surrounded bythe protective film 3. In addition, the first protective film 3 a isarranged between the lower side of the gate insulator film 5 and thechannel plane 7 of the substrate 1, and the second protective film 3 bis arranged between the second impurity diffusion region 2 b and thegate insulator film 5.

[0072] Furthermore, the present invention should not be limited to theabove described first through fifth preferred embodiments, but theinvention may be extended to the sixth preferred embodiment of atransistor according to the present invention which is shown in FIG. 10.In FIG. 10, the transistor has substantially the same construction asthose in some of the above described preferred embodiments, particularlyas that in the fifth preferred embodiment of a MIS transistor accordingto the present invention, in respect of the fact that a p+semiconductorsubstrate 1, a channel plane 7, a source region 2A, a drain region 2B, ahigh dielectric gate insulator film 5 and a gate electrode 6 areprovided.

[0073] In the sixth preferred embodiment of a transistor according tothe present invention which is shown in FIG. 10, each of electroderegions is provided with respective terminals, i.e., a gate terminal 16,a source terminal 17 and a drain terminal 18, via a low resistancecontact 15. In addition, a protective film 3 a is provided between thechannel plane 7 and the gate insulator film 5. Moreover, a protectivefilm 3 b is also provided between the gate electrode 6 and the side wall8 surrounding all of the low resistance contact 15 and the gate terminal16.

[0074] The gate insulator film 5 is formed so that Ox corresponds to 1.5nm or less. The low resistance contact 15 has a value of resistance of“Rcontact<10⁻⁸ Ωcm²”. The channel plane 7 is a very shallow channel (aretrograde channel) of “Rp˜15 nm, dRp˜7 nm”. In addition, the sourceregion 2A and the drain region 2B are formed so as to be a secondimpurity diffusion region 2B which has a low resistance of “Xj<10 nm,R<16 Ωμm” and which is elevated by a very small thickness.

[0075] With this construction, the sixth preferred embodiment of atransistor according to the present invention also has the gist of thepresent invention wherein the top surface of the source/drain region isarranged toward the gate electrode from a reference plane of the channelplane and toward the substrate from a reference plane of the bottomsurface of the gate electrode, and is one of the preferred embodimentsof a MIS transistor according to the present invention.

[0076] Referring to FIGS. 11 through 13E, the seventh preferredembodiment of a semiconductor device according to the present inventionwill be described below. First, a sectional structure of the seventhpreferred embodiment of a semiconductor device according to the presentinvention is shown in FIG. 11.

[0077] In FIG. 11, a gate electrode 114 of, e.g., a polycrystalline Si,an amorphous Si, TiN, W, Pt, RuO₂ or IrO₂, is formed on the top of asemiconductor layer 105 of, e.g., p-type Si, via a gate insulator film113 of, e.g., TiO₂, Al₂O₃, tantalum oxide film, barium titanate or leadzirconate titanate. Assuming that the thickness of a portion of the gateinsulator film 113 contacting the semiconductor layer 105 is t (nm) andthe relative dielectric constant thereof is ε, the relationship of t<1.3ε is satisfied.

[0078] In addition, the ion implantation or solid diffusion of P, Sb orAs into regions 105 on both sides of the gate electrode is carried outto be grown, and a source diffusion layer and a drain diffusion layer110, which have an opposite conductive type to that of the semiconductorlayer 105, are formed to form an n-type MISFET. Moreover, on the top ofthe source and drain diffusion layers 110, a conductive region 104 of,e.g., Si, SiGe or SiGeC, to which P, Sb orAs is added, is formed. Thisconductive region 104 is formed at a higher level than the interfacebetween the gate insulator film 113 and the semiconductor layer 105, andhas a so-called elevated source/drain structure.

[0079] Moreover, on the side wall wherein the gate electrode 114 of thegate insulator film 113 is not formed, an insulator film 109 of, e.g., asilicon nitride film, is formed. In addition, an insulator film 108 of,e.g., silicon oxide film, is formed between the insulator film 109 andthe conductive region 104. Moreover, on the top surface of theconductive region 104, on which the insulator films 108 and 113 are notformed, a conductive layer 115 of, e.g., cobalt silicide, nickelsilicide or titanium silicide, is formed. The feature of the seventhpreferred embodiment is that the top surface of the conductive region104 is formed at a lower level than that of the bottom of the gateelectrode 114. Thus, it is possible to hold a small capacitance betweenthe gate electrode 114 and the conductive region 104 and to provide asource/drain region elevated structure. In addition, it is possible todecrease the depth of junction of the conductive region 104 and toprovide a short channel effect, low resistance source/drain.

[0080] Moreover, on the top surface of the conductive layer 115, aninsulator films 111 and 112 of, e.g., a silicon oxide film, arelaminated. In order to form a contact 116 having a good shape even if itis difficult to etch the gate insulator film 113, it is desired that thetop surface of the gate insulator film 113 is lower than the top surfaceof the insulator film 112. Moreover, an insulator film 118 of, e.g., asilicon oxide film or a silicon nitride film, is formed on the top ofthe gate electrode 114, the gate insulator film 113 and the insulatorfilm 112. In addition, a contact electrode 116 of, e.g., apolycrystalline silicon, into which Al, P or B is doped, WSi, TiSi, W,AlSi, AlSiCu, Cu or TiN, is formed on the top of the gate electrode 114and on the top of the electrode 115.

[0081] Moreover, a polycrystalline silicon, into which Al, P or B isdoped, or a metal of WSi, TiSi, AlSi, AlSiCu, Cu or W is deposited onthe top of the contact electrode 116 to form a top wiring layer 117. InFIG. 11, while the contact electrode 116 and wiring layer 117 to thegate electrode have been shown on the same cross section as that of thecontact electrode 116 and wiring layer 117 to the source/drainelectrode, it is not always required to form these electrodes on thesame cross section, but these electrodes may be formed on differentcross sections, which are taken along different planes, as shown inFIGS. 12A and 12B.

[0082] Referring to FIGS. 13A through 13E, a method for producing theseventh preferred embodiment of a semiconductor device according to thepresent invention will be described below. First., a semiconductor layer105 having a p-type region having, e.g., a boron density of 10¹⁵ cm⁻³ isprepared. Then, the ion implantation and well diffusion of boron ofabout 10¹² to 10¹⁵ cm⁻³ into the p-type semiconductor layer 105 may becarried out to achieve a well diffusion to optimize the density of thesemiconductor layer 105. The energy of ion implantation is set to be,e.g., in the range of from 100 eV to 1000 eV. The density of these wellregions may be in the range of from 10¹⁵ cm⁻³ to 10¹⁹ cm⁻³. Then, anelement isolating region (not shown) of, e.g., an LOCOS isolation or atrench isolation, is formed.

[0083] Then, the ion implantation and well diffusion of boron or indiuminto the p-type semiconductor layer 105 may be carried out to optimizethe density of the semiconductor layer 105. Then, the surface of thesemiconductor layer 105 is oxidized or nitrided by, e.g., 3 to 50 nm toform a dummy gate insulator film 102, and a polycrystalline silicon filmserving as a dummy gate electrode 101 having a thickness of, e.g., 10 to200 nm is deposited on the whole surface. Moreover, after a siliconoxide film to be an insulator film 106 having a thickness of, e.g., 2 to200 nm, is deposited on the whole surface or formed by the oxidation ofthe polycrystalline silicon film, the polycrystalline silicon film to bethe insulator film 106 and the dummy gate electrode 101 is worked so asto reach the top of the insulator film 102 by the lithography and thereactive ion etching to form the dummy gate electrode 101. Then, afterthe silicon oxide film to be the insulator film 103 is deposited on thewhole surface so as to have a thickness of, e.g., 2 to 50 nm, it isworked by the anisotropic etching to leave the side insulator film 103on the side wall of the dummy gate electrode 101. Thereafter, theinsulator film 102 is etched using the insulator film 103 as a mask toexpose the semiconductor layer 105. Thus, the dummy gate electrode 101is surrounded by the side wall insulator film 103 and the insulator film106, which has been deposited immediately before the lithography, sothat it is easy to selectively grow a semiconductor in the source/drainlayer.

[0084] Then, as shown in FIG. 13A, a semiconductor layer 104 of Si, amixed crystal of SiGe or a mixed crystal of SiGeC, which has a thicknessof, e.g., 5 to 100 nm, is formed by the selective epitaxial growthmethod or selective deposition method. At this time, it is desired thatdoping is also carried out to add a donor impurity of As, Sb or P havinga density of 10¹⁶ to 10²¹ cm³ to the semiconductor layer 104 in order toform a low resistance, shallow junction. The semiconductor layer 104 maybe formed by causing, e.g., As of AsH₃ or P of PH₃, to be absorbed intothe surface of the semiconductor layer 105, and thereafter, by carryingout the selective epitaxial growth of, e.g., Si, a mixed crystal of SiGeor a mixed crystal of SiGeC.

[0085] In particular, if the semiconductor substrate has the plane {100}and if gate working is carried out by patterning the semiconductorsubstrate in parallel to the orientation <100>, the plane {311} isformed on the gate side wall portion as shown in FIG. 13A, so that it ispossible to form a structure which is farther from the gate side wall atan upper portion, so that it is possible to hold a small capacitancebetween the gate and source and between the gate and drain.

[0086] Then, there is added a step of, e.g., diffusing an impurity addedn-type region 110 into the p-type semiconductor layer 105 by heating ata temperature of 700 to 1100° C. in an atmosphere of Ar or N₂ for 0.01to 60 min as shown in FIG. 13B. In order to increase the current drivingpower, it is desired that the diffusion time is typically a period oftime that the n-type region 110 is formed below the dummy gate layer 101and formed so as to reach below a gate electrode 114 which will beformed layer.

[0087] The step of forming the semiconductor layer 104 and the n-typeregion 110 may be replaced with a step of ion-implanting As, P or SB of10¹³ to 10¹⁶ cm⁻² at an acceleration voltage of 1 to 100 eV to form ann-type region 110, and thereafter, selective-epitaxial-growing thesemiconductor layer 104. Alternatively, it may be replaced with a stepof forming an n-type region 110 by ion-implanting As, P or Sb of 10¹³ to10¹⁶ cm⁻² at an acceleration voltage of 1 to 300 eV after forming asemiconductor layer 105, to which no impurity is intentionally added.

[0088] Moreover, e.g., a silicon oxide film of 2 to 100 nm is depositedon the whole surface to form an insulator film 108. Then, e.g., asilicon nitride film of 10 to 300 nm is deposited on the whole surface,and an insulator film 109 is formed on the side wall of the sideinsulator film 108 cut by the anisotropic etching, so that the shapeshown in FIG. 13B can be obtained. The insulator film 108 is herein abuffer layer for the stress relaxation, etching selectivity and damagerelaxation of the insulator film 109. If there is particularly noproblem on the stress of the insulator film 109 and the etchingselectivity of the insulator film to the semiconductor layer 104, noinsulator film 108 may be provided.

[0089] It is desired that the sum of the thickness of the insulator film108 and the thickness of the side insulator film 103 be smaller than thethickness of the insulator film 102 since the insulator film 109 isexposed to define the width of the gate insulator film 113 when theinsulator film 102 is peeled off. The distance between the adjacentinsulator films 109 is set to be twice or more as large as the thicknessof a portion of the gate insulator film 113 contacting the semiconductorlayer 105. Moreover, after the insulator film 108 is removed from thesemiconductor layer by etching using the insulator film 109 as a mask, asilicide or metal is selectively formed on the semiconductor layer 104,which is to be a source/drain region, to form a source or drainelectrode 115. To achieve this, e.g., Ni, Co or Ti is deposited on thewhole surface by 0.01 to 0.03 μm, and a heat process of 600 degrees orhigher is carried out to selectively form NiSi, CoSi or TiSi on thesemiconductor layer 104, which is to be a source/drain region. Theremaining metal is etched with an aqueous solution of, e.g., sulfuricasid, to be removed.

[0090] Moreover, e.g., a silicon oxide film of 5 to 100 nm is depositedon the whole surface to form an interlayer insulator film 111. Then,e.g., a silicon oxide film, PSG, BPSG or BSG of 50 to 1000 nm isdeposited on the whole surface to be planarized by, e.g., the chemicalmechanical polishing, to form an interlayer insulator film 112.Thereafter, the upper portion of the dummy gate electrode 101 ispatterned by the lithography and anisotropic etching to etch parts ofthe interlayer insulator film 112, interlayer insulator film 111 andbuffer insulator film 108, insulator film 106 and side insulator film103 as shown in FIG. 13C to expose a part of the dummy gate electrode101.

[0091] At this time, a silicon oxide film is formed by the films 112,111, 108, 106 and 103, and the insulator film 109 is formed of a siliconnitride film, so that it is possible to selectively etch the films 112,111, 108, 106 and 103 while leaving the insulator film 109. After thisetching, it is desired that the resist, which has been used for thepatterning, be removed by, e.g., ashing or an aqueous solution ofsulfuric asid so as not to contaminate the gate insulator film 113 withmetals or organic substances.

[0092] Then, the whole dummy gate electrode 101 is removed by, e.g., thereactive etching using a gas containing HBr. At this time, the films112, 111, 108, 106 and 103 are left by holding the selectivity.Moreover, the whole dummy gate insulator film 102 of a silicon oxidefilm is removed by, e.g., dilute hydrofluoric acid, an aqueous solutionof ammonium fluoride, or HF solution. At this time, the films 108 and103 of a silicon nitride film are also etched and removed, and the sideinsulator film 109 of a silicon nitride film is not removed, so that thegate length can be defined by the interval therebetween. The step ofremoving the film 102 is preferably carried out by the wet etching, notthe ion etching, so as not to damage the semiconductor layer 105.

[0093] Then, a gate insulator film 113 of, e.g., TiO₂, Al₂O₃, tantalumoxide film, strontium titanate, barium titanate or lead zirconatetitanate, having a thickness of 10 to 200 nm is deposited on the wholesurface. Moreover, a gate electrode 114 of, e.g., a polycrystalline Si,an amorphous Si, TiNW, Pt, RuO₂ or IrO₂, having a thickness of 10 to 200nm is deposited on the whole surface to obtain the shape of FIG. 13D. Atthis time, the interlayer insulator films 111 and 112 are formed of asilicon oxide film similar to the film 102, and further retreats whenthe etching of the film 102, so that the etching opening increases inthe upper portion above the film 109. Therefore, this portion of theelectrode 114 is wider than the bottom portion thereof, so that aso-called T-shaped gate is formed. This shape is a desired shape todecrease the resistance of the gate electrode and to hold a smallcapacitance between the gate electrode and the source/drain electrode.In order to form a good T-shape, it is desired that the width of theopening is formed so that the edge of the interlayer insulator film 111remains on the side insulator film 109. In addition, when the uniformityof the gate insulator film 113 is not good, a shape wherein a part isnarrower in the laminated upward direction as shown in FIG. 13D isobtained. If the gate electrode 114 is deposited in this state, void isformed in the lower portion of the gate electrode as shown in FIG. 13D.

[0094] Then, etching is carried out by the chemical mechanical polishingmethod until the film 113 is exposed while the whole surface of the gateelectrode 114 is planarized. Moreover, the whole surface of the film 113is etched until the interlayer insulator film 112 is exposed, so thatthe shape of FIG. 13E is obtained. If the film 113 can be easilyanisotropic-etched at the subsequent contact forming step, the step ofremoving the film 113 can be omitted.

[0095] Thereafter, after the interlayer insulator film 118 of, e.g., asilicon oxide film, BSG, PSG or BPSG, having a thickness of, e.g., 20 to1000 nm, is deposited, a wiring contact 116 is formed by the lithographyand the reactive ion etching. The contact 116 may have a depth so thatthe contact 116 reaches the gate electrode 114 or the source/drainconductive electrode 115, and the contact 116 may be embedded and formedby depositing or selectively growing, e.g., an polycrystalline silicon,into which Al, P or B is doped, WSi, TiSi, W, AlSi, AlSiCu, Cu or TiN.Moreover, a metal of a polycrystalline silicon, into which Al, P or B isdoped, WSi, TiSi, AlSi, AlSiCu, Cu or W, having a thickness of 20 to 500nm is deposited to form an upper wiring layer 117. Thus, the process iscompleted.

[0096] According to a method for producing the seventh preferredembodiment of a MIS transistor according to the present invention, sincethe impurity of the source/drain electrode is activated to form asilicide before the gate insulator film 113, it is not required to carryout a process for deteriorating the characteristics of the gateinsulator film 113, such as a high temperature head process and hydrogenannealing, after forming the gate insulator film. Therefore, it ispossible to achieve a process having high reliability.

[0097] Moreover, the width of the gate electrode facing thesemiconductor region 105 is (width of dummy gate 101)+(thickness ofinsulator film 103)*2+(thickness of insulator film 108)*2−(side wallthickness of gate insulator 113)*2, so that it can be smaller than thewidth of the dummy gate 101. Therefore, it is possible to provide asmaller gate length than that in the lithography by adjusting the widthsof the insulator film 103 and the insulator film 108.

[0098] This structure is shown in FIGS. 12A and 12B which are plan viewsof a unit MISFET and which show the positional relationship between thegate electrode 114, the source/drain region 110 and the channel region.In both drawings, reference number 119 denotes an element isolating filmof, e.g., a LOCOS isolation or a trench isolation. These drawings alsoshow the position of the contact 116 by circles, and suppose a casewhere one contact is formed in each of the gate, source and drain. Thesemiconductor region is sandwiched between two source/drain electrodes110 and chain lines therebetween, and is a rectangular region surroundedby this and a solid line of the gate electrode 114. The boundary of aportion formed below the gate electrode 114 is shown by chain lines.

[0099] In FIG. 12A, the width of the lower portion of the gate electrode114 shown by a dotted line is set to be constant on the semiconductorregion surrounded by the element isolation 119. Thus, even if thealignment in the lithography of the gate electrode is shifted invertical directions, it is possible to always obtain a constant gatelength, so that the transistor characteristic can have resistance to aregistration error. FIG. 12B shows a modified example of a pattern ofthe gate electrode, wherein a gate length (=a) on the boundary betweenthe element isolation 119 and the semiconductor region is longer than agate length (=b) in the semiconductor region. With respect to the gateinsulator film 113 formed of a deposited film, the thickness depositedon the bottom of the groove increases as the width of the opening of thegroove increases. Therefore, with the structure of FIG. 12B, the gateinsulator film on the boundary between the element isolation 119 and thesemiconductor region can be greater than the flat portion, so that it ispossible to improve the dielectric breakdown voltage and leakage currentcharacteristic of this portion. When the trench isolation is used as theelement isolating film 119, if the element isolating film 119 is etchedat, e.g., the step of etching the dummy gate electrode 102, to form theelement isolating film 119 below the semiconductor region, thesemiconductor region is convex toward the element isolating film 119 tocause the increase of electric field, so that there is a problem in thatthreshold deteriorates. Therefore, this problem can be solved by thestructure of FIG. 12B.

[0100] Furthermore, the present invention should not be limited to theabove described preferred embodiments. In the above describedembodiments, the method for forming the insulator films 12, 111, 112,113, 102, 103, 106, 108, 118 and 109 may be any one of an oxide filmforming method using thermal oxidation, a method for forming an oxidefilm, into which oxygen is injected by a low acceleration energy ofabout 30 keV, a method for depositing an insulator film and a method fordepositing a silicon nitride film, or a combination thereof. The methodfor forming the element isolating films and the insulator filmsthemselves may be any one of other methods for converting silicon into asilicon oxide film or a silicon nitride film, e.g., a method forimplanting oxygen ions into deposited silicon, or a method for oxidizingdeposited silicon. Of course, this insulator film may be a siliconnitride film, a tantalum oxide film, a ferromagnetic film of strontiumtitanate, barium titanate or lead zirconate titanate, a monolayer filmof a paraelectric film, or a composite film thereof.

[0101] In the embodiments, while the p-type Si substrate has been usedas the semiconductor layer 7 and 105, the present invention should notbe limited thereto, but an n-type Si substrate, an SOI substrate, a GaAssubstrate or an InP substrate may be used. The present invention is notonly applied to the n-type MISFET, but it may also be applied to ap-type MISFET. In this case, in the above described embodiments, n-typeand p-type may be replaced with p-type and n-type, respectively, and thedoped impurities, As, P and Sb, may be replaced with any one of In andB. In the case of ion implantation, As, P and Sb may be replaced withany one of In, B and BF₂.

[0102] The gate electrode 10, 114 and 6 may be formed of amono-crystalline silicon, a polycrystalline silicon, a porous silicon,an amorphous silicon, a mixed crystal of SiGe, a mixed crystal of SiGeC,a metal or alloy, such as GaAs, W, Ta, Ti, Hf, Co, Pt and Pd, a silicidethereof, TaN, TiN, or a conductive nitride. The gate electrode 10, 114and 6 may have a laminated structure thereof. Moreover, the presentinvention can be embodied in various ways without departing from theprinciple of the invention. The dummy gate 10 is preferably formed ofSiGe or SiGeC so that a high etching selectivity to the source and drainregions 2 is kept during the removed process of the dummy gate 10.

[0103] According to the seventh preferred embodiment of a MIS transistorand a method for producing the same according to the present invention,since the inclined face is formed so as to extend from the top surfaceof the semiconductor layer serving as the source/drain region to thechannel plane, it is possible to insure the distance from the lower endof the gate electrode, so that there is a peculiar advantage in that itis possible to hold a smaller capacitance between the gate and sourceand between the gate and drain.

[0104] In addition, the shape of the gate electrode is a T-shape, sothat there are peculiar advantages in that it is possible to reduce theresistance of the gate electrode and it is possible to hold a smallcapacitance between the gate electrode and the source/drain electrode.

[0105] As described above, according to a MIS transistor and a methodfor producing the same according to the present invention, it ispossible to reduce the resistance of the impurity diffusion layerconstituting the source/drain, and it is also possible to reduce theparasitic capacitance of the gate, so that it is possible toconsiderably improve the switching speed of the transistor.

What is claimed is:
 1. A MIS transistor comprising a semiconductorsubstrate, source/drain regions formed on the substrate, and a gateelectrode provided above a channel region between the source/drainregions, wherein the top surfaces of said source/drain regions formed onsaid semiconductor substrate are arranged toward said gate electrodefrom a reference plane of a channel plane in said semiconductorsubstrate, the top surfaces of said source/drain regions are arrangedtoward said channel plane from a reference plane of an interface betweena gate insulator film formed on said channel plane and said gateelectrode, and a dielectric constant of said gate insulator film ishigher than that of silicon oxide.
 2. A MIS transistor as set forth inclaim 1 , wherein a groove is formed in the top surface of saidsemiconductor substrate and has a bottom surface serving as said channelplane, said gate insulator film being formed in an opening of saidgroove via a protective film, said gate electrode being arranged on thetop of said gate insulator film, said source/drain regions beingarranged on both sides of said channel plane, so that a predeterminedrelationship between the top surfaces of said source/drain regions, saidchannel plane and said interface is established.
 3. A MIS transistor asset forth in claim 1 , wherein the top surfaces of said source/drainregions laminated in places which sandwich said channel plane on saidsemiconductor substrate therebetween is arranged toward said gateelectrode from a reference plane of said channel plane, and the topsurfaces of said source/drain regions are arranged toward said channelplane from a reference plane of said interface between said gateinsulator film formed on said channel plane via a protective film andsaid gate electrode.
 4. A MIS transistor as set forth in claim 1 ,wherein the top surfaces of said source/drain regions provided so as tosandwich said channel plane therebetween is elevated from said channelplane to be arranged toward said gate electrode, and the top surfaces ofsaid source/drain regions have a substantially flat surface having alevel which is elevated and arranged toward said gate electrode, and aninclined surface which is inclined from said level of said flat surfaceto a level of said channel plane.
 5. A MIS transistor as set forth inclaim 4 , wherein said gate electrode surrounded by said gate insulatorfilm provided on the upper side of said channel plane has a crosssection of a T shape, the lower side of which is tapered via a stepportion.
 6. A MIS transistor as set forth in claim 1 , wherein said gateelectrode surrounded by said gate insulator film provided on the upperside of said channel plane has a cross section of a T shape, the lowerside of which is tapered via a step portion.
 7. A MIS transistor as setforth in claim 1 , wherein said gate insulator film includes a metaloxide film.
 8. A MIS transistor as set forth in claim 7 , wherein saidmetal oxide film includes any one of titanium oxide film, aluminum oxidefilm and tantalum oxide film.
 9. A MIS transistor as set forth in claim1 , wherein said gate insulator film has a predetermined dielectricconstant higher than that of an aluminum oxide film.
 10. A MIStransistor comprising a semiconductor substrate, source/drain regionsformed on the substrate, and a gate electrode provided above a channelregion between the source/drain regions, wherein the top surfaces ofsaid source/drain regions provided so as to sandwich said channel planetherebetween is elevated from said channel plane to be arranged towardsaid gate electrode, and the top surfaces of said source/drain regionshave a substantially flat surface having a level which is elevated andarranged toward said gate electrode, and an inclined surface which isinclined from said level of said flat surface to a level of said channelplane; and wherein said gate electrode surrounded by said gate insulatorfilm provided on the upper side of said channel plane has a crosssection of a T shape, the lower side of which is tapered via a stepportion.
 11. A method for producing a MIS transistor comprising asemiconductor substrate, source/drain regions formed on the substrate,and a gate electrode provided above a channel region between thesource/drain regions, said method comprising the steps of: selectivelyforming an oxide film on said semiconductor substrate; using theselectively formed oxide film as a mask to carry out etching to form agroove; laminating a semiconductor layer in said groove to polish thetop surfaces of said oxide film and said semiconductor film, andthereafter, removing said oxide film; using said semiconductor film as amask to diffuse an impurity in the surface of said semiconductorsubstrate to form a grooved impurity diffusion region including thebottom of said groove; arranging a gate insulator film of a highdielectric film in a groove portion of said grooved impurity diffusionregion so that the top surface of said gate insulator film is arrangedfarther from said semiconductor substrate than the top surface of saidimpurity diffusion region other than said groove portion; and forming agate electrode on the top surface of said gate insulator film.
 12. Amethod for producing a MIS transistor comprising a semiconductorsubstrate, source/drain regions formed on the substrate, and a gateelectrode provided above a channel region between the source/drainregions, said method comprising the steps of: selectively forming asemiconductor layer on said semiconductor substrate; using theselectively formed semiconductor layer as a mask to diffuse an impurityin the surface of said semiconductor substrate to form an impuritydiffusion region including an elevated impurity diffusion regionelevated from a channel plane which is formed on the surface of themasked semiconductor substrate; forming an oxide film on the side of thesurface of said elevated impurity diffusion region to use saidsemiconductor layer as a stopper to polish the surface of said oxidefilm, and thereafter, removing said semiconductor layer; forming a gateinsulator film of a high dielectric film in a region bordering saidelevated impurity diffusion region and said oxide film so that the topsurface of said gate insulator film is arranged farther from saidsubstrate than the interface between said impurity diffusion region andsaid oxide film; and forming a gate electrode on the top surface of saidgate insulator film.
 13. A method for producing a MIS transistorcomprising a semiconductor substrate, source/drain regions formed on thesubstrate, and a gate electrode provided above a channel region betweenthe source/drain regions, said method comprising the steps of:selectively depositing semiconductor layers serving as source/drainregions, which sandwich a region serving as a channel plane on saidsemiconductor substrate therebetween, so that an inclined surface isformed between the top surface of said semiconductor layers and saidchannel plane; forming a dummy gate insulator film and a dummy gateelectrode including a second semiconductor layer on said channel plane,which borders the selectively formed semiconductor layers, by atechnique including at least a lithography; using said secondsemiconductor layer as a mask to diffuse an impurity in the surface ofsaid semiconductor substrate to form impurity diffusion regions;removing said dummy gate electrode, which is formed on a portion servingas said channel plane sandwiched between said impurity diffusionregions, by etching; depositing an insulator film of a high dielectricfilm on the whole surface of the exposed channel plane to form a gateinsulator film, which has a cross section of a grooved space at thecenter thereof; and depositing a gate electrode on the top surface ofsaid gate insulator film, which is formed on the whole surface so as tohave a grooved space at the center thereof, to form a gate electrodehaving a cross section of a T shape.